In March, as coronavirus widened its global sweep, one health statistic quickly flattened: influenza cases. In the Southern Hemisphere, flu season would have been just taking off, but cases were virtually nonexistent. “Never in my 40-year career have we ever seen rates … so low,” says Greg Poland, an influenza expert at the Mayo Clinic. Although researchers need to study the reasons further, several told Scientific American that coronavirus prevention measures—handwashing, mask wearing and social distancing—are working against flu transmission. If those measures continue, Poland says, countries could see the most dramatic drop in influenza cases in modern human history. U.S. health experts still recommend flu shots, however, because not everyone in the country is observing measures to contain the virus and because COVID-19 could perhaps be more threatening in people who contract flu.